Antigen presentation is an obligatory step in the development of specific[unreadable] antibody and cellular immune responses that protect individuals from[unreadable] infection. Understanding this process should lead to novel approaches to[unreadable] control immune responses including the development new and more effective[unreadable] vaccines. The theme of this project remains the analysis of how antigens[unreadable] (Ags) are processed and presented to T lymphocytes. The central hypothesis[unreadable] of this project is that class I Ag processing involves the cleavage of Ags[unreadable] into peptides through the action of intracellular proteanases. There are[unreadable] 3 specific Aims: 1. What is the role of ubiquitin and the 265 proteasome in class I Ag[unreadable] presentation? The goals of this Aim are: (i) To evaluate whether and to[unreadable] what extent Ub and the 26S proteasome play a role in the processing of[unreadable] endogenous Ags for class I presentation; and, (ii) To test the hypothesis[unreadable] that the rate of degradation of Ags in the cytosol is a critical parameter[unreadable] that influences the efficiency of class I presentation. The experimental[unreadable] approach is to analyze whether blocking or enhancing degradation by the[unreadable] Ub-proteasome pathway of degradation affects class I-restricted Ag[unreadable] presentation. These studies will define the role of a major catabolic[unreadable] pathway in Ag processing. In addition, these experiments will define how[unreadable] degradation may control the immunogenicity of intracellular Ags and could[unreadable] provide a rationale strategy for designing more active vaccines. [unreadable] 2. Does a form of the proteasome generate appropriate peptides for class[unreadable] I presentation? The goal of this Aim is to examine whether the proteasome[unreadable] generates antigenic peptides and whether its activity/specificity is[unreadable] immunologically-regulated. The experimental approach will be to analyze in[unreadable] cell free systems the activity and specificity of the various forms of the[unreadable] proteasome from normal, mutant or interferon-stimulated cells. These[unreadable] experiments will define whether the 205 or 265 proteasome produce one or[unreadable] both appropriate cleavages for immunogenic peptides and what role the MHC-[unreadable] encoded subunits may play in this process. 3. How does a subset of APCs process exogenous Ags for MHC class I[unreadable] presentation? The goal of this Aim is to define the apparently novel pathway through which some APCs processes exogenous Ag. The experimental approach will use mutant (targeted gene disruption) and cloned-lines of[unreadable] these APCs in studies that will directly follow the fate of Ag and in experiments using modified-Ags and selective inhibitors to probe the key steps in this pathway.[unreadable] [unreadable]